1. Field of the Invention
The present invention relates generally to magnetic actuators, and more particularly to a strong magnetic thrust force type actuator for producing a relatively large magnetic thrust for use within an industrial robot, or the like.
2. Prior Art
Conventional linear pulse motors comprise a primary member and secondary member. Generally the primary member is an electrically supplied member, or in other words, an electromagnetically excited member. Accordingly, the primary member travels along the secondary member in a linearly reciprocating to and fro direction when a pulse current is supplied to the primary member. In this case, the primary member is movable, while the secondary member is stationary, however, either the primary or secondary member can be movable.
FIG. 1 shows a conventional linear pulse motor. Numeral 1 designates a secondary member which is an elongate magnetic material plate, the upper side of which forms rectangular teeth 1a and grooves 1b along the longitudinal direction at a constant pitch. Above the teeth 1a and grooves 1b, primary member 2 is positioned at a predetermined distance from secondary member 1 so as to define a space therebetween. This primary member 2 is movably supported by means of a supporting member such as, for example, a roller, wheel, or the like.
Primary member 2 comprises core 4 for the A-phase and core 5 for the B-phase, there being provided magnetic poles 4a and 4b for core 4, and magnetic poles 5a and 5b for core 5; coils 6a and 6b wound around magnetic poles 4a and 4b, respectively; coils 7a and 7b wound around magnetic poles 5a and 5b, respectively; permanent magnets 8 and 9 disposed upon cores 4 and 5, in which the N-pole of permanent magnet 8 faces the upper surface of core 4, while the S-pole of permanent magnet 9 faces the upper surface of core 5; and cover plate 10, formed by means of a magnetic material, which covers permanent magnets 8 and 9. The lower side of magnetic pole 4a has pole teeth 14a and grooves 14c, each of which is formed at a constant pitch. The lower sides of magnetic poles 4b, 5a, and 5b have similar pole teeth 14b, 15a, and 15b , and grooves 14d, 15c, and 15d, respectively.
Assuming that the constant pitch of rectangular teeth 1a is indicated by means of the distance P, each of the pole teeth 14b, 15a, and 15b is shifted by means of a distance of P/4 with respect to rectangular teeth 1a as shown in FIG. 2, and the lower surfaces of these teeth are positioned at a distance G from the upper surface of teeth 1a.
Accordingly, in turn, by supplying a pulse current to coils 6a, 6b, 7a, and 7b, a magnetic flux is generated, respectively. This magnetic flux and the magnetic flux from permanent magnets 8 and 9, in turn, act upon respective magnetic poles 4a, 4b, 5a, and 5b, allowing primary member 2 to travel along secondary member 1 in the longitudinal direction.
Next, in FIG. 2(a) to FIG. 2(d), primary member 2 traveling along secondary member 1 is described as a result of being based upon a two-phase exciting system which supplies a pulse current to coils 6a and 6b in one group, and coils 7a and 7b in the other group. This pulse current energizes magnetic poles 4a, 4b, 5a, and 5b.
In FIG. 2(a), by supplying the pulse current from terminal 6c to terminal 6d through means of coils 6a and 6b as shown by means of the direction of the arrows, and also, by supplying this pulse current from terminal 7d to terminal 7c through means of coils 7a and 7b, as shown by means of the direction of the arrows, the magnetic flux generated from coil 6a is added to the magnetic flux generated from permanent magnet 8 at magnetic pole 4a for the A-phase, and each of these magnetic fluxes at magnetic pole 4b for the A-phase opposes the other. On the other hand, the magnetic flux generated from coil 7a is added to the magnetic flux generated from permanent magnet 9 at magnetic pole 5a for the B-phase, and each of these magnetic fluxes at magnetic pole 5b for the B-phase opposes the other. Magnetic flux .phi..sub.1 is thus generated in the direction of the arrows as shown in FIG. 2(a). As a result, the magnetic field acts upon pole teeth 14a and 15a facing rectangular teeth 1a so as to produce a magnetic thrust.
In FIG. 2(b), by supplying the pulse current to coils 6a and 6b in the same direction as shown in FIG. 2(a), and also, by supplying a pulse current to coils 7a and 7b in the opposite direction with respect to the direction shown in FIG. 2(a), magnetic flux .phi..sub.2 is thus generated in the direction of the arrows as shown in FIG. 2(b). As a result, the magnetic field acts upon pole teeth 14a and 15b facing rectangular teeth 1a so as to produce magnetic thrust.
In FIG. 2(c), by supplying the pulse current to coils 6a and 6b in the opposite direction with respect to the direction shown in FIG. 2(b), and by supplying the pulse current to coils 7a and 7b in the same direction as shown in FIG. 2(b), magnetic flux .phi..sub.3 is thus generated in the direction of the arrows as shown in FIG. 2(c). As a result, the magnetic field acts upon pole teeth 14b and 15b facing rectangular teeth 1a so as to produce the magnetic thrust.
Similarly, in FIG. 2(d), by supplying the pulse current to coils 6a and 6b in the same direction as shown in FIG. 2(C), and to coils 7a and 7b in the opposite direction with respect to the direction shown in FIG. 2(c), magnetic flux .phi..sub.4 is thus generated in the direction of the arrows as shown in FIG. 2(d). As a result, the magnetic field acts upon pole teeth 14b and 15a facing rectangular teeth 1a so as to produce the magnetic thrust.
Accordingly, the pulse current is, in turn, supplied to respective coils 6a, 6b, 7a, and 7b in the successive order of such FIG. 2(a), FIG. 2(b), FIG. 2(c), and FIG. 2(d). This allows primary member 2 to travel toward the right in the drawings, that is, from magnetic pole 4a to magnetic pole 5b, while when the pulse current is, in turn, supplied to the respective coils in the decreasing order of such FIG. 2(d), FIG. 2(c), FIG. 2(b), and FIG. 2(a), primary member 2 is caused to travel toward the left in the drawing, that is, from magnetic pole 5b to magnetic pole 4a.
Generally, such a linear pulse motor is thus used without a closed-loop control circuit for accurately positioning an object at a certain position, which makes the driving device useful for office automation equipment such as, for example, printers. However, it is difficult to use this type of device in industrial robots because of the high magnetic thrust required.
According to the linear pulse motor described above, in FIG. 2(a), while generating the magnetic thrust at magnetic poles 4a and 5a, each of the magnetic fluxes is counteracted at magnetic poles 4b and 5b, respectively. A resultant magnetic thrust is thus not generated at magnetic poles 4b and 5b. A similar magnetic thrust is generated at magnetic poles 4a and 5b in FIG. 2(b), magnetic poles 4b and 5b in FIG. 2(c), and magnetic poles 4b and 5a in FIG. 2(d). As a result, the area of magnetic poles 4a, 4b, 5a, and 5b which can generate the magnetic thrust is only 50% of the total pole area. This area is significant in that it produces the magnetic thrust.